Catheters formed of a biocompatible plastics material are sometimes implanted in patients to relieve various symptoms and/or to assist in medical procedures. For example, central venous catheters have been implanted into a patient's vein during vascular surgery. One problem associated with such implanted catheters, however, is that a fibrin sheath (which is a deposit of fibrin and platelets) may form on the implanted catheter, initially at the entrance site into the vein and then along the length of the catheter. While it usually takes weeks to months for the fibrin sheath to form, it has been reported to form in as little as 24-48 hours following implant.
The fibrin sheath can cause catheter dysfunction, usually being manifested by the physician being able to infuse through, but not to aspirate from, the catheter. Intraluminal urokinase may then be administered several times to exclude the possibility of intraluminal clotting. If intraluminal urokinase treatment is ineffective, fluoroscopy may then be performed to allow the physician to evaluate catheter tip location and to obtain evidence of fibrin sheath formation.
Once the presence and extent of the fibrin sheath have been identified, the physician must take the necessary steps to remove the sheath from the implanted catheter. While it is conceivable that the implanted catheter may be removed and replaced surgically, it is more desirable for the fibrin sheath to be removed without surgical removal of the implanted catheter.
Presently, there are basically two approaches which may be employed without removal of the implanted catheter. The first approach involves introducing percutaneously a goose-neck snare (e.g., a snare device generally disclosed in U.S. Pat. No. 5,171,233 to Amplatz et al, the entire content of which is incorporated expressly hereinto by reference) into the patient's groin area. The snare is then advanced through the patient's femoral vein to the catheter implant site, at which time it is manipulated so that the snare encircles the distal end of the implanted catheter so that the fibrin sheath may be stripped therefrom. While the fibrin sheath which is stripped from the distal end of the implanted catheter travels to the patient's lung, surgical removal has been shown to result in embolization as well.
Another technique that has been employed to strip fibrin sheaths from the distal ends of implanted catheters is to introduce a J-tipped wire intraluminally through the implanted catheter. Rotation of the J-tipped wire about the distal end of the implanted catheter will thus strip a portion of the fibrin sheath therefrom. While this technique is advantageous since the implanted catheter serves as a guide passageway (i.e., separate incisions to access the femoral vein are unnecessary), the J-tipped wire is typically only capable of removing less than all of the fibrin sheath from the implanted catheter due to its size limitations.
What has been needed in this art, therefore, is a medical device which is capable of being guided intraluminally through an implanted catheter, but which is capable of removing substantially all of the fibrin sheath that may have formed at the catheter's distal end. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in medical devices having a snare loop for removing patient-internal material from an implanted catheter (e.g., a fibrin sheath which may form at the distal end of a venous catheter) which may be inserted intraluminally through the catheter during a medical procedure, the snare loop being capable of retroflexing in a proximal direction when extended beyond the distal end of the catheter so that it encircles the implanted catheter's distal region.
According to one embodiment of the invention, such retroflexing is accomplished by incorporating at least one pair of bend regions in the guide wire which are axially spaced-apart from one another. These bend regions will cause the shape-memory guide wire to flex upon advancement of the device beyond the distal end of the catheter so that the snare loop is capable of retroflexing around the catheter's distal end.
Another embodiment of this invention includes a number of proximally directed struts having one end attached to the distal end of the guide wire. A draw wire extends from the guide catheter and is flexed in a proximal direction so as to be connected to the snare loop which is positionally held by the terminal ends of the struts. When the draw wire is pulled proximally, the struts are moved toward parallel alignment with the guide catheter which, in turn, contracts the snare loop. Advancement of the device and/or withdrawal of the draw wire will therefore allow the contracted snare loop to strip a distal segment of the fibrin sheath from the implanted catheter's terminal end. A membrane may optionally be connected to the struts so that the removed fibrin sheath segment may be captured and removed proximally through the lumen of the implanted catheter.
Further aspects and advantages of this invention will become apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.